Tunneling magnetoresistive devices as read heads in hard disk drives

Abstract

Hard Disk Drive read heads moved from GMR to Tunneling Magnetoresistive (TMR) Devices as a way to enhance head SNR in order to keep up with advanced linear densities. TMR technology was further extended by the transition from amorphous alumina tunneling barriers to crystalline MgO barriers lattice matched to adjacent BCC magnetic layers resulting in much higher MR ratios. Enhanced side shielding using Junction Shield and reduced shield to shield spacing were additional enablers that increased track and linear density capabilities of TMR heads. TMR heads gained additional momentum and complexity by the introduction of two dimensional recording heads that boosted head SNR by up to 3 dB. As the RA of the tunneling barriers is reduced, overcoming spin torque noise presents itself as a further challenge to be addressed. As device dimensions are scaled down, magnetic thermal noise can only be overcome by increasing the moment of the free layer which may already start establishing the final density point achievable by TMR heads.